The present invention generally relates to an elastic bushing or mount for vehicles and specifically in a coupling portion of a vehicle such as suspension bushing which attenuates or dampens vibrations and shock forces.
Rubber isolation isolators for vehicles take the form of powertrain mounts, front and rear suspension bushings and differential mounts or the like to isolate the transmission of road induced vibratory forces into the vehicle or to isolate vibratory forces induced from the powertrain. Conventional cylindrical vibration damping bushings for suspension systems which are generally made of a rubber member are well known in the prior art.
In an automobile, the rubber isolator is primarily in shear mode for low load displacements. However, as the load on the rubber isolator increases dramatically, the shear capacity of the rubber member may be exceeded and to prevent this, the isolator has a rubber stop portion which becomes loaded in compression to assist the rubber mount to absorb the load and limit the shear load on the rubber isolator member. This generally creates a discontinuity in the load absorbing characteristics of the mount such that the vehicle operator will notice a sudden shift in load absorbing characteristics. This is undesirable in today""s vehicles and many approaches have been taken to try and solve the problem.
One approach used to solve this problem is the use of hydraulic isolation mounts. Such devices use an annular rubber block and an annular rubber diaphragm. The annular parts are provided with at least two recesses, and are configured and assembled such that the recesses complement one another to form first and second fluid-filled working chambers. The chambers are sealed with respect to the environment and joined to one another, in a manner allowing fluid to pass, by at least one damping passage. High frequency, low amplitude vibration is absorbed by the rubber block. Low frequency, high amplitude forces cause the liquid in the main chamber to move into an auxiliary chamber to absorb these forces. While this influences the force versus displacement response of a particular design, such approaches have not solved the basic problem of isolating vibratory forces over a broad vibration spectrum, and they have been found to be expensive to make.
Another approach used in the prior art is the use of a hydro-bush. An example of such a device is U.S. Pat. No. 5,503,376. The hydro-bush is a hydraulically dampened rubber spring sleeve containing two annular parts. However, it is difficult to decouple the vibration forces and thus these devices have limited use. The isolation capabilities are limited and are dependent on the solid elastomeric properties of the rubber block.
Other approaches have generally focused on lowering the friction co-efficient on the rubber surface such as by adding wax into the rubber composition or adding liquid silicone oil into the rubber composition or the like. However, it is found that the degree to which the friction co-efficient is decreased is usually not significant enough to dampen vibration over the entire frequency spectrum and such approaches are effective only within narrow temperature ranges. Thus, there is a need to provide a low cost, simple but effective solution to this problem.
The present invention is drawn to a bushing which solves this problem. The bushing includes a bracket with a cavity, the cavity having an inner surface. A core member is disposed in the cavity. A pair of elastomeric members are between the core and the inner surface. One of the pair of elastomeric members having a modulus that is greater than the other of the pair of elastomeric members so that one of the pair of elastomeric members absorbs higher amplitude and lower frequency vibration and the other of the pair of elastomeric members absorbs low amplitude and high frequency vibration.
A primary object of the present invention is to use a volume incompressible material and volume compressible material to make a bushing.
Another object of the present invention is to employ foamed elastomer as a vibration isolator which is also an assembly aid to simplify the manufacturing process.
A still further object of the present invention is to use a pair of elastomeric members of which one is a solid elastomer to absorb low frequency and high amplitude vibration and the other is a foamed elastomer to absorb high frequency and low amplitude vibration.
These and other features of the present invention will become apparent upon consideration of the following description and the appended claims with reference to the accompanying drawings all of which form part of the specification.